I think basically you either got a big chest with genetics or not. No matter what I do I can't grow my chest. On the other hand I don't ever work out arms and they are my best feature. It is just my genetics. My brother is the complete opposite. He has a good chest but no arms. He hardly ever works out chests and has tried everything he can to grow his arms but can't. I think we are all just stuck with our genetics (unless you get some roids probably)

You can try doing shrugs with a barbell and an underhand grip - go with the feeling, adjust the widness of the grip in such a way that it suits you. Just try to feel it in the upper pecs as you are lifting the weight, simple as that.